Going back to work part time. advice

I am currently on 12-weeks maternity leave at 80% pay until early March. I had my first baby in mid-December. I work in marketing.

I would like to discuss the following things with my boss and would love advice on how to do approach the topic:

1. Taking an additional 2-4 weeks, unpaid

2. Coming back part-time. My company currently has part-time and remote employees so this wouldn’t be foreign.